Transformer Design Calculation Excel

 

Fundamentals of Power Electronics Chapter 15: Transformer design22 Determine wire sizes Fraction of window area allocated to each winding: α 1 = 4A 8A = 0.5 α 2 = 1 5 20 A 8A = 0.5 (Since, in this example, the ratio of winding rms currents is equal to the turns ratio, equal areas are allocated to each winding) Wire areas: A w1 = (0.5)(0.5)(0.297) =. Distribution transformer calculations spreadsheet provides fast calculations for the following: Determining the MV/LV transformer rating, calculating overcurrent protection device rating on the low voltage side of the transformer, calculating the prospective short circuit current and Calculating natural ventilation openings sizes required for the transformer room. Design of the joints of magnetic cores has a profound impact on core losses and transformer efficiency. The paper introduces a finite element methodology for the analysis of transformer joints. The proposed technique consists in the application of certain boundary conditions for the excitation of the joints. Secondary Current Calculation Size of Secondary Wire for Transformer Design Calculation a2= (4.2 A/ 2.3) = 1.83 mm2 From the standard copper wire, table it can be seen that wire of this thickness is of 15 gauge. 10 Electrical MS Excel Spreadsheets for Electrical Engineers. This section is dedicated to tools every electrical engineer can use in daily work. These spreadsheets below will make your job much more easier, alowing you to shorten the time used for endless calculations of cables, voltage drop, various selections of circuit breakers, capacitors.

An SMPS transformer becomes apparent at the output of all forward-mode converter. Converters applying the forward, push-pull, half-bridge and full-bridge topologies are typically forward-mode converters. Therefore, calculation of the output inductance employs the equivalent techniques for any 4 of these kinds of widely used topologies. The actual intent behind the output inductor is always to retain power for the load in the period just about every switching cycle whenever the power devices (BJTs, MOSFETs or IGBTs) are switched off. The electrical operation of the SMPS transformer is always to combine the rectangular switching pulses (pulse width modulated signals with changing duty cycle) into DC. The capacitor positioned after the inductor smooths the DC into ripple free DC.

The calculation of the SMPS transformer is pretty straightforward. More often than not, a self-gapped toroid core can be used. Gapped ferrite cores (the types employed for ferrite transformers, eg ETD39) may possibly be accustomed without problems.

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The formula for determining the output inductance is:

L(min) = [Vin(max) - V(out) x T(ON) / 1.4 x Iout(min)

Vin(max) = maximum voltage next to the output rectifier within that specific output.
Vout = output voltage.
Toff(est) = anticipated ON time of power device at the maximum input voltage.
Iout(min) = least heavy anticipated load current to achieve that output.

Determined from the above formula is L(min) which is the minimal recommended inductance, below which the core is going to be drained of flux at the least rated load current for that specific output.

Make sure you plan a circuit that permits for functioning without having any load. Unquestionably, you can not replace zero for Iout(min) because that might contribute to an L(min) figure of infinity. And surely, that actually isn’t imaginable, could it be?

Which means that, what you need to accomplish is that you ought to decide upon the very least permissible current.

Work with a resistor load along at the output of the power source in order that should you have hardly any load, this resistor load delivers the bare minimum load.

Iout(min) needs to be significant enough that L(min) certainly is not exceedingly big; it additionally should not be exceedingly massive which may induce excessive power deficits, therefore a negative efficiency, on account of the power dissipation in the output resistor.

Commonly, this resistor is termed a dummy load whose exclusive objective is always to offer the minimal load if there is hardly any other load at the output of the converter / supply of power.

Seeing that we understand the minimum needed inductance, we should comprehend the number of turns to incorporate on our core.

Through the datasheet of the core, you will discover the AL magnitude. This signifies the inductance upon each turns squared:

AL = L/N^2

L will be the inductance and N would be the amount of turns. Implementing M as the argument:

L = √ L/AL

Thus, here is the formula which may be utilized to figure out the quantity of turns when we identify the preferred inductance.

Occasionally you probably will not be familiar with the AL valuation. You possibly will not find out the component spec the core you own thereby unable to identify the datasheet.

No matter what the explanation, it is possible to experimentally identify the AL valuation.

Execute several turns and determine using an L meter, the inductance. After that, measure the inductance for a sets of many different number of turns.

Do it again for all these selected numbers of turns. Therefore, determine the inductance for, as an example, 5, 10, 20, 40 turns after which for each and every, determine the AL value. Obtain the average AL value.

One of the things that can be done is, you might sketch a graph of L against N2. The gradient of the most effective match line could possibly be the AL value. You might also mathematically determine the gradient of the “regression line”. Exercise whatsoever course you realize is the quickest.

At this moment let’s check out a case in point to solve just what you’ve understood until at this instant.

Let’s stipulate that our converter is a half-bridge converter.

The input voltage for the converter will be different out of 150VAC (212VDC) to 250VAC (354VDC). Output voltage from the converter can be 14VDC. The turning frequency is 50kHz.

Transformer primary: 26 turns
Transformer secondary: 4+4 turns

The formula for computing the minimal essential inductance is:

L(min) = [Vin(max) - V(out) x T(ON) / 1.4 x Iout(min)

Transformer

We will have to evaluate the output voltage with the transformer secondary at 354VDC input, that may be our optimum input voltage.

We’ll believe that the voltage drop as a result of the rectifier diode is 1V. Consequently the typical output voltage within the transformer secondary is 15V. Transformer turns ratio (primary: secondary) = 26:4 = 6.5

Thus, at any time typical secondary voltage is the same as 15V, typical voltage across transformer primary is 6.5 * 15V = 97.5V. In case duty cycle was 100%, voltage across transformer primary could well be 177V (50% the DC bus voltage - consider half-bridge topology). Therefore, the duty cycle is (97.5/177)*100% = 55%.

Average output voltage on transformer secondary will be 15V which has a duty cycle of 55%. Consequently, maximum output voltage is 15V/0.55 = 27.3V, and then there is assumed a diode reduction of 1V. Therefore, Vin(max) is 26.3V.

At optimum input voltage, duty cycle will probably be smallest. This can be any time the off time is going to be the greatest.

We now have determined a duty cycle value of 55% - this is actually the minimum duty cycle number. Since switching frequency is 50kHz, period of time is 20µs. The off period is 0.45 * 20µs = 9µs. Which is our Toff(est).

Let’s stipulate that the particular minimal load is going to pull 500mA current. Using a 14V output and 500mA current, the electricity dissipated in the output resistor will likely be:

P = VI = 14 x 0.5 W = 7 Watts

That is certainly a great deal of power! In case it’s agreeable, by all means employ a 500mA minimum load. If you decide to fetch the minimum load all the way down to 250mA, you trim down power dissipation (above) to 3.5W.

Therefore now we have figured out all the essential variables. Let’s connect these into the formula.

L(min) = (26.3 - 14) x 9 x 10^-6 / 1.4 x 0.25

= 316uH

This is often the bare minimum expected inductance. Feel free to use an inductance higher than the minimum number established, considering that, well you determined the minimum essential inductance.

Let’s believe we’ll exploit an inductance of 450µH. Let’s stipulate that we’ve picked out a toroid core with an AL valuation on 64nH per turn squared.

To begin with, the expected inductance is 316µH that could be equivalent to 316000nH.

Therefore the preferred range of turns is:

It can be possibly 70 or 71 turns. This is often for 316µH.

Transformer design calculation excel format

Regarding 450µH:

Let's make this around 84 turns.

So...now you know How to Calculate SMPS Transformer Turns at home, which you can apply this easy solution in order to determine the necessary output inductance for any converter in which employs the forward, push-pull, half-bridge or full-bridge topology. It’s effortless and also Lets hope I have personally had the opportunity to enable you to comprehend without a doubt. I want to appreciate your feedback and opinions!

Converting power from high voltage sources is very challenging, especially because you need to design the isolation as well as the transformer. Hi, I'm Surinder Singh. I'll show you how WEBENCH tools can help you overcome these challenges. Let us take an example from everyday life. I need to charge the handheld device, but the power that is available to me is coming from the wall at an AC voltage, which is typically a very high voltage. In this scenario, what are my key requirements? Of course, I need to make sure that my design balances efficiency, footprint, and cost, and, of course, I'm able to regulate to the desired DC level, and, very importantly, I am able to provide electrical isolation. When there is no direct conduction path from the high voltage input side to the low voltage DC side, we say that a power converter is isolated. And isolation is important because if the electrical shorts or component failures or surges, they are not transmitted to the other side. And this protects both the human operator as well as the equipment. One of the most popular topologies for converting power from high voltages is the flyback topology. Central to the idea of the operation of the flyback is the flyback transformer. And the flyback transformer provides both isolation, as well as it provides an inductor for storage of the energy. And this makes a topology a very, very popular topology. Let's take a look at the operation of the flyback converter. The flyback transformer on the primary side is connected to a semiconductor switch. On the secondary side, there is a diode, which provides the rectification function. The primary is directly connected to a DC source. But if the input to our converter is not a DC but an AC, we can convert it into DC using full-bridge rectification. Now, let's take a look at how the flyback operates. When the MOSFET is on, the DC source is directly connected to the primary side. Hence, the current in the primary will keep increasing. This increasing current will store the energy into the magnetic core. And in this stage, the output diode is not conducting because it is reverse-biased. When the MOSFET turns off, the same energy which is just stored in the magnetic core is now transferred into the secondary side and the diode forward biases. Sometimes, we have a third stage of operation, in which the magnetic energy goes to zero. And this stage is called the Discontinuous Mode, or the DCM mode. A typical flyback converter also has other components. We talked about the AC/DC full-bridge rectifier. But there is a control IC, which has to drive the external MOSFET. And because they could be ringing on the drain of the MOSFET, you need to design these numbers. And of course, from the output side, we need to regulate the voltage. So some sensing mechanism has to happen, which is usually through an optocoupler, which provides the feedback back to the control IC. This control IC, of course, needs power too, so this power is sometimes generated from the same transformer using auxiliary windings. The flyback transformer, as you can see now, is the core of how the flyback works. And unlike the transformer in other scenarios, this transformer is really an coupled inductor. So it's stores the energy during one phase and delivers it to the output in the other phase. The flyback is a complex topology to design. The biggest challenge lies in designing the flyback transformer itself. The designer must choose from a large variety of cores and bobbins available and at the same time making sure that the electrical targets are satisfied and the other constraints are respected. So let's look at some of these targets and constraints in more detail. The primary inductance, which determines the ripple current, needs to be of a certain value. And this depends on the turns ratio, which is a design parameter, and the core cross-section area and the air gap. So if the number of turns increase, the primary inductance also increases. The magnetic material itself goes through a process called saturation. So we need to make sure that our design is such, which means that our maximum current and the number of turns is such that we do not hit the saturation. In fact, we stay away from it and set a target of a Bmax. Next, we need to make sure that the power dissipated into the copper wiring is less than a certain target value. This power itself is estimated by knowing what the DC resistance of the copper wire itself is. And as shown in this formula, this is proportional to the connectivity of the copper and the length of the copper wire. The length of the copper wire itself depends on the number of turns and the mean length per turn, which is a property of the core. A loss constraint is really a physical constraint, which says that the area available inside the core must be utilized such that all the wiring can fit into there. And since there is a certain amount of space loss, because of insulation and the circular shape of the wire, the fill factor cannot completely be 1. So its typically between 0.5 and 0.9. From these four constraints, we can eliminate the design unknowns of number of turns, air gap, and wire cross section and express it in the form of the following inequality. The left side depends only on the physical dimensions of the core. And it is called the core geometrical constant, Kg. Its units are length to the power of fifth. The right hand side depends on the property of the design, which is the electrical and the magnetic properties. This inequality is very powerful, because it tells us how to select the cores. That means, the core Kg must be larger than the design Kg. For example, if we need to have larger amount of current in our design, which means that the required Kg from the cores would shoot up. Now, we take all these constraints, and we can design the rest of the transformer. So we can now determine the number of turns in the primary. And based on the turns ratio, we can set the number of turns in the secondary and the auxiliary. And we can also specify the so-called inductance factor, which we have so far expressed in terms of the air gap. And at this point, our transformer is ready to be designed. This transformer design algorithm, if done manually, is not only laborious and time-consuming to do but will also give suboptimal results. Here, the WEBENCH Power design tools can be of great help. So let's see how we can create designs using very WEBENCH tools. Let us design with the UCC28C42. So go to the product folder of this page, where you will find a WEBENCH panel on which you can put in your design input/output conditions. Click on Open Design. And in a few seconds, you'll be presented with the entire design done in the form of a summary. You'll see your schematic, your bill of materials, operating values presented to you. The power loss contributions are automatically calculated. And you can view them in charts. And you can view the other operating values in the Operating Values tab also. The bill of materials can be downloaded from the Bill of Materials tab. And you can print out the PDF of your entire design, as well as share it with your coworkers. Now, let's look at the transformer that the tool created for us. So click on the schematic, where you'll see the symbol for the transformer. Click on it, and it will open up a window showing you the transformer that the tool designed for you. In this window, you can see the core part number that has been selected, the bobbin, as well as all designing information and the electrical characteristics that the tool computed for you. If you're happy with this, you can continue your design with this transformer. But if you wanted to explore more cool bobbin combinations, click here, which will take you to this page. Here, you can look at other combinations of cores and bobbins, which will work for your design, and the key characteristics of those cores and bobbins. And specifically, if you wanted to look at Kg, the geometrical factor, you can look at here. Now, let's do something interesting. Let's change the design conditions from 2 amps to 1 amp. So we're basically reducing the amount of power that we need by about 1/2. So go back to the schematic, click on the Explore the Core Bobbin Combination. And you go back and look at the Kg's. So now, you'll find that the Kg value is less than what we had required for a 2-amp design. A more closer comparison also reveals that the winding ratios are different, the wires used are different, and the primary inductances that the tool calculated are different for the 2-amp and the 1-amp design. You'll also notice something very interesting, that the 1-amp design results in transformers which are cheaper, have a smaller footprint, and a smaller Kg. This is all what we expected. But the tool has done it for us. Once you are satisfied with your design, go back to the transformer design page and download the transformer report. This PDF report contains all the information that you need to manufacture your transformer-- so things like number of turns, winding diagrams, core and bobbin part numbers. You can handle this report to your manufacturing department and get your transformer fabricated. So what we have seen is, the WEBENCH design tools in a matter of minutes can take your input/output specifications down to a report for your transformer. I enjoyed giving this presentation. Please explore WEBENCH transformer designer for your next isolated and high voltage design. Thank you.

Description

Design your isolated high-voltage power supply as well as the transformer. In this video we will take you through the design process of designing an isolated AC/DC or DC/DC power supply. We will highlight the key design constraints for designing the transformer and show you how the WEBENCH tool designs the transformer for you. Using this video, for example, you will be easily be able to design a low-voltage DC power for a handheld device from a high-voltage AC power socket using the Flyback topology, while maintaining low cost, high efficiency and small size.

Key take-aways:

  • Learn why high voltage power supplies need isolation and how it is implemented

  • Understand the operation and key advantages of the popular Flyback topology

  • Get insight into the design constraints of the Flyback transformer (FBT), or the coupled Inductor, and see how the WEBENCH® Designer designs the transformer with these constraints

  • Learn how to use WEBENCH® Designer to design an isolated, high-voltage power supply and its transformer

  • Walk through an exercise using the UCC28C42 BiCMOS current-mode PWM controller

Transformer Design Calculation Excel

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